The effects of low-dose oral contraceptives on coagulation and fibrinolysis in two high-risk populations: young female smokers and older premenopausal women.

A study was undertaken to determine the effect of a low-dose oral contraceptive on the coagulation and inhibitory system of coagulation in 22 young healthy women who smoke and in 15 nonsmoking healthy women between the ages of 34 and 41. Smokers showed statistically significant oral contraceptive-related procoagulant alterations in prothrombin time, thrombin time, and fibrinogen antigen. Antithrombin III antigen and activity were significantly reduced, whereas plasminogen antigen and activity were increased. Inhibitor and fibrinolytic activity was either unaffected or enhanced by oral contraceptives in women over the age of 34: antithrombin III activity was unchanged, plasminogen antigen and activity increased (p less than 0.0007), and alpha 2-antiplasmin was significantly reduced (p less than 0.07). Whereas usage of oral contraceptives in young smokers may initiate biochemical changes in favor of thrombogenesis, their usage in nonsmoking older women enhanced fibrinolysis and had a neutral effect on inhibition and a minimal procoagulant effect.